Rocker shaft with diamond-like carbon coating

ABSTRACT

A rocker shaft for a valve train of an internal combustion engine, including: a substantially cylindrical outer circumferential surface; and a layer of amorphous hydrocarbon deposited on the substantially cylindrical outer circumferential surface. The rocker shaft is arranged to engage a rocker arm such that the rocker arm is at least partially rotatable about the rocker shaft. A method of forming rocker shaft for a valve train of an internal combustion engine, including: forming a substantially cylindrical outer circumferential surface; and depositing a layer of amorphous hydrocarbon on the substantially cylindrical outer circumferential surface. The rocker shaft is arranged to engage a rocker arm such that the rocker arm is at least partially rotatable about the rocker shaft.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 61/857,315, filed Jul. 23, 2013, which application is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a rocker shaft for a vehicular valve train having a diamond-like carbon coating.

BACKGROUND

A valve train for a vehicular valve train, for example, a valve train for an internal combustion engine, in particular an overhead cam configuration or an overhead valve configuration, includes rocker arms for actuating engine valves. The rocker arms swivel about rocker shafts. Friction between the rocker arms and the rocker shaft decreases engine efficiency during engine valve actuation by the rocker arm. Using rolling element bearings to reduce the friction undesirably adds to the weight of the valve train.

For some valve train configurations, the rocker shaft delivers pressurized oil to the rocker arms. Rolling element bearings cannot be used in the preceding configurations to reduce friction between the rocker shaft and rocker arms since the bearings would provide leakage gaps and the presence of pressurized oil in a rolling element bearing would increase friction associated with the bearing.

SUMMARY

According to aspects illustrated herein, there is provided a rocker shaft for a valve train of an internal combustion engine, including: a substantially cylindrical outer circumferential surface; and a layer of amorphous hydrocarbon deposited on the substantially cylindrical outer circumferential surface. The rocker shaft is arranged to engage a rocker arm such that the rocker arm is at least partially rotatable about the rocker shaft.

According to aspects illustrated herein, there is provided a rocker shaft assembly for a valve train of an internal combustion engine, including: a rocker shaft with a substantially cylindrical outer circumferential surface and a layer of amorphous hydrocarbon deposited on the substantially cylindrical outer circumferential surface; and a rocker arm radially disposed about the substantially cylindrical outer circumferential surface; in contact with the layer of amorphous hydrocarbon; and at least partially rotatable about the rocker shaft.

According to aspects illustrated herein, there is provided a method of forming rocker shaft for a valve train of an internal combustion engine, including: forming a substantially cylindrical outer circumferential surface; and depositing a layer of amorphous hydrocarbon on the substantially cylindrical outer circumferential surface. The rocker shaft is arranged to engage a rocker arm such that the rocker arm is at least partially rotatable about the rocker shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments are disclosed, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, in which:

FIG. 1 is a perspective view of a portion of a valve train including a rocker arm and a rocker shaft with a diamond-like carbon coating;

FIG. 2 is a cross-sectional view generally along line 2/5-2/5 in FIG. 1 showing an example channel;

FIG. 3 is a schematic block diagram of a portion of a power train for an internal combustion engine including the valve train of FIG. 1;

FIG. 4 is a perspective view of a valve train including a rocker arm and a rocker shaft with a diamond-like carbon coating; and,

FIG. 5 is a cross-sectional view generally along line 2/5-2/5 in FIG. 1 showing an example solid rocker shaft.

DETAILED DESCRIPTION

At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical, or functionally similar, structural elements of the disclosure. It is to be understood that the disclosure as claimed is not limited to the disclosed aspects.

Furthermore, it is understood that this disclosure is not limited to the particular methodology, materials and modifications described and as such may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the present disclosure.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. It should be understood that any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure.

FIG. 1 is a perspective view of a portion of a valve train including a rocker arm and rocker shaft 100 with a diamond-like carbon coating.

FIG. 2 is a cross-sectional view generally along line 2/5-2/5 in FIG. 1 showing an example channel.

FIG. 3 is a schematic block diagram of a portion of a power train for an internal combustion engine including the valve train of FIG. 1. The following should be viewed in light of FIGS. 1 through 3. Rocker shaft 100 in a portion of valve train 101 includes substantially cylindrical outer circumferential surface 102 and layer 104 of amorphous hydrocarbon deposited on the substantially cylindrical outer circumferential surface. Note that in FIG. 2, thickness T of layer 104 has been exaggerated for purposes of illustration. Rocker shaft 100 is arranged to engage rocker arm 106 such that rocker arm 106 is at least partially rotatable about rocker shaft 100. For example, rocker arm 106 is partially rotatable about shaft 100 to actuate engine valve 108.

In an example embodiment, the amorphous hydrocarbon in layer 104 includes metal-free amorphous hydrocarbon. In an example embodiment, the amorphous hydrocarbon in layer 104 include metal-free amorphous hydrocarbon with sp² and sp³ hybridized carbon. Further detail regarding a layer of amorphous hydrocarbon, metal-free amorphous hydrocarbon, or metal-free amorphous hydrocarbon with sp² and sp³ hybridized carbon is provided in commonly-owned U.S. Pat. Nos. 7,363,894 and 8,161,925, which patents are incorporated in their entirety herein.

In an example embodiment, for example as shown in FIG. 2, rocker shaft 100 includes channel 110 for flowing pressurized oil, for example, to rocker arm 106.

FIG. 5 is a cross-sectional view generally along line 2/5-2/5 in FIG. 1 showing an example solid rocker shaft. In an example embodiment, for example as shown in FIG. 5, rocker shaft 100 is solid in cross-section, that is, shaft 100 is free of a channel, such as channel 110 shown in FIG. 2.

In an example embodiment, rocker shaft 100 is part of rocker shaft assembly 112 for valve train 101 of internal combustion engine 116. Assembly 112 includes rocker arm 106.

In an example embodiment, valve train 101 includes push rod 120, valve lifter 122, and camshaft 124. As is known in the art, the rotation of camshaft 124, in particular cam lobe 126, displaces valve lifter 122 and push rod 120 to rotate rocker arm 106 about rocker shaft 100. As noted above, rocker arm 106 actuates valve 108. In an example embodiment, engine valve 108 includes valve stem 128 in contact with rocker arm 106 and valve spring 130. In an example embodiment, a lash adjuster (not visible in the figures) is located within valve lifter 122.

The following describes a method of forming a rocker shaft for a valve train of an internal combustion engine. Although the method is presented as a sequence of steps for clarity, no order should be inferred from the sequence unless explicitly stated. A first step forms a substantially cylindrical outer circumferential surface. A second step deposits a layer of amorphous hydrocarbon on the substantially cylindrical outer circumferential surface. The rocker shaft is arranged to engage a rocker arm such that the rocker arm is at least partially rotatable about the rocker shaft.

In an example embodiment, the amorphous hydrocarbon includes metal-free amorphous hydrocarbon. In an example embodiment, the amorphous hydrocarbon includes metal-free amorphous hydrocarbon with sp² and sp³ hybridized carbon.

In an example embodiment, a fourth step forms a channel in the rocker shaft for flowing pressurized oil.

FIG. 4 is a perspective view of a portion of a valve train including a rocker arm and rocker shaft 200 with a diamond-like carbon coating. Shaft 200 is included in a portion of valve train 201. In an example embodiment, rocker arm 206 includes lash adjuster 218. The discussion regarding rocker shaft 100 and valve train 101 is applicable to rocker shaft 200 and valve train 201. For example, elements 200, 206, 208, 210, 220, 222, 224, 226, 228, and 230 in FIG. 4 are substantially analogous to elements 100, 106, 108, 110, 120, 122, 124, 126, 128, and 130 in FIG. 1.

It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. 

1. A rocker shaft for a valve train of an internal combustion engine, comprising: a substantially cylindrical outer circumferential surface; and, a layer of amorphous hydrocarbon deposited on the substantially cylindrical outer circumferential surface, wherein: the rocker shaft is arranged to engage a rocker arm such that the rocker arm is at least partially rotatable about the rocker shaft.
 2. The rocker shaft of claim 1 wherein the amorphous hydrocarbon includes: metal-free amorphous hydrocarbon.
 3. The rocker shaft of claim 1, wherein the amorphous hydrocarbon includes: metal-free amorphous hydrocarbon with sp² and sp³ hybridized carbon.
 4. The rocker shaft of claim 1, wherein the rocker shaft includes a channel for flowing pressurized oil.
 5. The rocker shaft of claim 1, wherein the rocker shaft is free of a channel for flowing pressurized oil.
 6. A rocker shaft assembly for a valve train of an internal combustion engine, comprising: a rocker shaft including: a substantially cylindrical outer circumferential surface; and, a layer of metal-free amorphous hydrocarbon deposited on the substantially cylindrical outer circumferential surface; and, a rocker arm: radially disposed about the substantially cylindrical outer circumferential surface; in contact with the layer of amorphous hydrocarbon; and, at least partially rotatable about the rocker shaft.
 7. The rocker shaft assembly of claim 6, wherein the amorphous hydrocarbon includes metal-free amorphous hydrocarbon.
 8. The rocker shaft assembly of claim 6, wherein the metal-free amorphous hydrocarbon includes metal-free amorphous hydrocarbon with sp² and sp³ hybridized carbon.
 9. The rocker shaft of claim 6, wherein rocker shaft includes a channel for flowing pressurized oil to the rocker arm.
 10. The rocker shaft of claim 6, wherein the rocker shaft is free of a channel for flowing pressurized oil.
 11. A method of forming rocker shaft for a valve train of an internal combustion engine, comprising: forming a substantially cylindrical outer circumferential surface; and, depositing a layer of amorphous hydrocarbon on the substantially cylindrical outer circumferential surface, wherein: the rocker shaft is arranged to engage a rocker arm such that the rocker arm is at least partially rotatable about the rocker shaft.
 12. The method of claim 11, wherein the amorphous hydrocarbon includes: metal-free amorphous hydrocarbon.
 13. The method of claim 11 wherein the amorphous hydrocarbon includes: metal-free amorphous hydrocarbon with sp² and sp³ hybridized carbon.
 14. The method of claim 11, further comprising: forming a channel in the rocker shaft for flowing pressurized oil.
 15. The method of claim 11, further comprising: forming the rocker shaft without a channel for flowing pressurized oil. 